This project is designed to apply the experimental detector techniques of nuclear and particle physics to the development and enhancement of an economical multi-modality imaging system to observe and follow the metabolism of tagged biological molecules in the small animals Our preliminary work has been applied to studies of the uptake of the cocaine analog, RTI-55, in the mouse. More recently we have begun to study the distribution of tagged insulin in normal and hyperglycemic mice. Such detectors allow one to follow the distribution of ligands of interest over periods of minutes to days after injection. Because the studies are carried out in vivo, without need to sacrifice the animal, we can follow the metabolism and elimination of the substance under study for as long as is biologically interesting. A parallel and equally important goal of this research is the increased participation of undergraduate physics students in research that applies the techniques of physics and mathematics to studies in the field of biology. William and Mary has enjoyed an excellent record at training premedical students. The research described here has already involved eight William and Mary physics majors in research with applications to the health fields during the past two years. One of those students has gone on to graduate training in the field of medical imaging. Another has entered medical school. Three more are presently applying to graduate schools to carry out research in medical imaging. Two others will not graduate until next academic year. The basic elements of the imaging system under development include scintillation detectors similar to those used in experiments in elementary particle physics. Highly segmented ("pixellated") slabs of scintillation material are mounted on special position sensitive photomultipliertubes (PSPMT). That combination can be used to image a mouse or other small animal injected with tagged biological ligands. A small x-ray system is used in combination with those detectors to allow the correlation of structural and functional information on an animal under observation. An additional goal of this work will include the development of a system of moderate cost suitable for use by a wide range of biological research groups with need for only modest support by nuclear physicists or technicians.